Juping Tu, Jiayi Li, Yong Wang, Yun Zhao, Jinlong Liu, Junjun Wei, Liangxian Chen, Jianjun Zhang, Yang Lü, Chengming Li
Producing inch-scale, binder-free ultrahard diamond presents a formidable challenge due to the limitations of the conventional high-pressure and high-temperature method. Here, we report a customized microwave plasma chemical vapor deposition technique with high-frequency gas-switching control. By periodically introducing nitrogen, a transient local non-equilibrium growth mode is established, enabling the synthesis of free-standing ultrahard diamond wafers up to 3 mm thick and 5 inches in diameter. The wafers exhibit a Vickers hardness of ~208.3 GPa, comparable to the hardest nano-twinned diamonds, and show exceptional wear resistance-abrasive ratio ~7 times higher than polycrystalline diamond substrate. High-resolution transmission electron microscopy reveals an ultra-dense three-dimensional interlocked stacking fault network (density up to 4.3×10¹² cm⁻²), contributing to superior mechanical properties. This process also allows deposition on commonly used three-dimensional tool surfaces. This work provides a scalable strategy for producing ultrahard, inch-scale diamond suitable for demanding applications in precision machining, semiconductor and aerospace industries.